For example, when an imaging device such as a camera with automatic focusing attempts to continuously focus a target object with a focusing lens, movement of the target object within an image or a scene change in an image should at once be detected to determine the position of the target object within the image. On the other hand, when focus on a target object can be maintained without re-selection of the target object, the processing of re-selecting the target object or re-focusing the target object may make an operator feel uncomfortable.
The conventional camera is proposed to employ a method of automatic object detection in an image by detecting the variation in brightness within the image. The proposed method cannot detect a scene change with a small variation in brightness when the scene changes in response to panning the camera by an operator. The camera accordingly cannot keep in focus the target object.
The conventional camera, once focus is achieved, fixes a lens position of the focusing lens so as to detect a scene change on the basis of the variation in a brightness and a focus evaluation value. When a threshold value is set to the variation in brightness and focus evaluation values for avoiding any erroneous detection of a scene change through fine movement of a target object, the camera sometimes cannot detect a scene change in which a new small object appears in front of the focused target object, since the variation in the brightness and focus evaluation values is small.
Further, the conventional camera fixes a lens position of the focusing lens once a focus is achieved, so that the camera detects a scene change so as to re-select the target object when the focused target object moves back and forth. In this case, the position of the target object within the image is maintained so that a focus can be achieved at the same position. Accordingly, the overall process of re-selecting the target object may waste time. It is preferable to cope with back and forth movement of the target object by simply moving the focusing lens to a lens position allowing the maximum focus evaluation value without re-selection of the object.